Error 503 - An Issue?

Server returns a 503 (service unavailable) status code when it is unable to handle the request due to a temporary overloading or maintenance of the server.

Does this have any impact when a search engine crawls you? Using Google Webmaster it said that it found one error, i.e. the Error 503 - my question is, this won't suddenly make google think that my site is not working and won't return?

I've seen googlebot respider pages that always and in every case return 500 errors almost daily. I figured that after, say 100 days of errors in a row it might get the hint... that this page will more than likely never work again. But it keeps on trying as long as the page is there, or until it's redirected.